The present invention relates to a metering unit for granular material.
Besides so-called single grain sowing units, distribution devices for granular material or sowing devices that operate volumetrically are known in numerous embodiments. In particular, grain conveyance can, in this context, be carried out by means of an airflow carrying the grains. By the metered feeding of the grains into the airflow, it is possible to vary the volumetric flow of sowed grains. Nevertheless, the grains are often deposited unevenly at the seed drill coulters, as both the precision of the grain metering and the regulation of the airflow can only be influenced to a certain extent, which leads to disadvantages in the growing space allocated to the individual plants.
A device for separating and discharging granular material that is universally applicable for different grain sizes and seed types is known from DE 36 33 955 A1. For this purpose, a rotating, slender hollow cylinder with recesses forming cells at its open front end, a stationary outer cover, and a cover ring arranged within the hollow cylinder are proposed. A storage hopper is separated by a wall from the hollow cylinder, which wall has an opening for the passage of a limited quantity of material to be separated. The length of one of the recess forming cells should equal the length of two or more grains to be separated. Furthermore, a suction opening is provided close to the rear boundary surface of the recesses. The fast rotating hollow cylinder picks up a few grains from the grain supply with each recess such that the outer cover covers the recesses in the filling section and prevents the grains from falling out. The centrifugal force presses the grains into the recesses, while a brush wiper provides for excess grains to be wiped off and fall back into the supply. An outer boundary wall ends in the further course of movement of the hollow cylinder such that grains that are not retained in the recesses by the suction pressure are released outward by centrifugal forces and are fed back into the supply. An additional pneumatic wiper can support this grain separation. At the point of release, the negative pressure is cut off such that the grains are released from the recesses by centrifugal force and gravitational force.
Furthermore, EP 0 636 306 A1 discloses a distribution device for granular material, such as seeds. The distribution device comprises a housing with an inner cover surface taking the form of a circular path, an inlet opening for granular material, a conveyor device for the granular material, which conveyor device rotates concentrically in the housing, and also an outlet opening. In its outer area, the conveyor device has a plurality of openings, which, in a first housing section and together with the inner cover surface of the housing, form a pocket, into which the grains are pushed and circularly conveyed by centrifugal forces supported by the conveyor device. The inlet opening leads into a second housing section. The first housing section and the second housing section are separated by a stationary, contoured disk. The contour of the disk is intended to provide for wiping off excess grains that are being transported in the pockets of the conveyor device. These grains are then available for conveyance again.
The mentioned metering devices are either modified single grain sowing units, which, although they do allow precise grain separation are, however, limited in their processing capacity and in their grain volume flow in comparison to volumetrically metering seed-drill machines and/or are relatively elaborate and prone to failure regarding their structure and their mode of operation. The additional devices that have become known, which are intended to improve the even release of the seeds in volumetrically metering machines, however, do not reach the separation quality of conventional single grain sowing units.
WO 2013/186175 A1, finally, discloses a distribution device for granular material, which distribution device can be employed, in particular, as a sowing unit in a sowing machine. This known unit comprises a housing with an inner cover surface taking approximately the form of a circular path and/or of a circle segment. Rotating concentrically in the housing is a disk-shaped conveyor device for the conveyed granular material or the conveyed seeds, as the case may be. An outlet opening extends approximately tangentially to the inner cover surface of the housing. At its outer periphery, the disk-shaped conveyor device has openings or shoulders, which in connection with the rotation of the disk and with the airflow provide for the circular movements of the grains along the inner cover surface. In a separating section, only one single grain remains in each opening or at each shoulder, as the case may be, of the disk-shaped conveyor device by means of the adjusted contour of the inner cover surface of the housing and under the influence of centrifugal forces, while the excess grains are discharged and fed back into the first housing section for being conveyed again.
The last mentioned sowing unit has proven successful in practice and enables precise grain separation in volumetric grain conveyance, however, it requires accurate adjustment of the recesses or openings located along the periphery of the rotating conveyor disk to the respective grain type being conveyed and sowed. When relatively small grains are conveyed in openings that are too large-sized, it is hardly possible to separate them precisely, as there will frequently be two, three, or more grains being conveyed in each opening and being released at the same time through the outlet opening. If, in contrast, the openings or recesses are too small, the separating unit will completely fail and will release the grains just as unevenly as they were previously transported into the inlet opening. In order to prevent these problems, it is inevitable in practice to exchange the conveyor disk rotating in the housing when changing the type of grains and to replace it for accordingly appropriately sized disks. As a multi-row sowing machine has a separate metering unit of the construction type described for each seed drill coulter, a corresponding number of sets of replaceable metering disks are required, which not only causes costs, but also requires a high logistic effort from the respective user.
DE 38 31 042 A1 further discloses a device for the axial shifting of a machine part being rotatable in relation to a stationary machine body. A threaded bushing is rotatably arranged at the stationary machine body. In this instance, a bearing of the rotatable machine part is axially fixed by an outer layer, and the inner layer of the bearing is fixed on the rotatable machine part. For the axial setting of the device, an adjusting spanner can be applied to the engagement surface. In order to disengage a locking screw, the bushing can be twisted in the machine part, thus effecting the axial adjustment of the bushing. Another possibility for axial adjustment of a cell wheel is also disclosed in DE 195 44 237 A1.